Method for the preparation of flexible carbon fibre



United States Patent '0.

3,285,696 METHOD FOR THE PREPARATION OF FLEXIBLE CARBON FIBRE YasugoroTsunoda, Kumamoto-ken, Japan, assignor to Tokai Denkyoku Seizo KabushikiKaisha, Tokyo, Japan No Drawing. Filed Apr. 5, 1963,'Ser. N0.270,807Claims priority, application Japan, Aug. 25,1960, 35/ 36,145 3 Claims.(Cl. 23-209.1)

This application is a continuation-in-part of my earlier previouslycopending application, Ser. No. 97,461 filed March 22, 1961, nowabandoned.

This invention relates to methods for the preparation of flexible heatresisting and corrosion resistant fibre.

The corrosion resistance of carbon and graphite against variouschemicals and the heat resistance of carbon and graphite aresubstantially perfect excepting when these materials are placed in anoxidizing atmosphere. It has therefore been considered desirable toproduce woven fabric made of carbon or graphite but which also hassatisfactory mechanical strength It is known that if a fibre (forexample, cotton or Orlon) containing carbon is heated at hightemperatures (700-3,000 C.) in an inert gas atmosphere such as nitrogenor argon, the fibre retains the shape it had before-the heat treatment.Fibre obtained in this way is, however, so brittle that yarn and wovenfabric made of such fibre are of no practical use.

It is an object of this invention to prepare fibrous carbon and graphitehaving improved properties.

Other objects and advantages of this invention will be apparent from thefollowing description of some preferred embodiments.

The invention provides a method for the preparation of heat resistingand corrosion resistant fibre, characterized in that fibre, made of amaterial selected from the group consisting of acrylonitrile polymer andacrylonitrile copolymer prepared from less than 85 mol percent ofacrylonitrile and not more than 15 mol percent of a monovinyl compound,is heated at a temperature from 180 to 550 C. in an oxygen-containingatmos phere for a time sufficient to blacken the fibre. Then theblackened material is carbonized and if necessary graphitized by aconventional method.

The fibrous carbon and graphite prepared by the methd mentioned. aboveare mechanically stronger and more flexible than those made by directcarbonization or graphitization without the pretreatment according tothe invention.

According to the invention, a product such as -a filament, staple, orbatting is made of the fibre which is made from acrylonitrilehomopolymer or copolymer produced by copolymerizing not less than 85 molpercent of acrylonitrile with not more than 15 mol percent of amonovinyl compound such as methyl acrylate, methyl methacrylate, vinyl,acetate, vinyl chloride, vinylidine chloride, 2-methyl-5-vinyl pyridineor the like. This product is heated for 5-60 minutes at 180-230 C. in anoxygen containing atmosphere such as air. The temperature and timenecessary for heating depend on the thickness of the fibre or wovenfabric but, for convenience, it is determined by the degree ofblackening of the fibre. Polyacrylonitrile becomes yellowish, brown andblack successively by heating in air, but yellowish and brown fibres arenot suit-able for the purpose of this invention since their carbonizedor graphitized products are brittle.

Then the blackened. fibre is carbonized at a temperature between700-1200 C. for not less than 1 hour in an inert atmosphere to form acarbonized fibre. If a more heat resistant and corrosion resistant fibreis required, the carbonized fibre is graphitized at a temperature bep.JCC

tween 1200-3000 C. in an inert atmosphere to form a graphitized fibre.Said inert atmosphere may be an inert gas or a packing material such asgraphite, carbon black and silica. 1

Example I 'Staple of acrylonitrile copolymer containing 4 mol percent ofmethyl acrylate (yarn countings #48, two-ply) was heated in air at 220C. for 3 hrs. in order to blacken it completely. Then the blackenedfibre was heated in a nitrogen atmosphere at 1,000 C. for 1 hr. Theproduct was not broken by bending, its tensile strength being above 60g./yarn. The same staple was heated in air at 220 C. for 20 minutes and.a dark brown fibre was obtained. Then the fibre was heated in a nitrogenatmosphere at 1,000 C. for 1 hour. A carbonized fibre resulted which wasso brittle that it was easily broken by bending and its tensile strengthwas 20 g./yarn. On the other hand, the tensile strength of the productwhich was made merely by direct heating of the same fibre ofpolyacrylonitrile in a nitrogen atmosphere at 1,000 C. for 1 hr. was assmall as about 6-11 g./yarn. The latter product wasrelatively'inflexible so that it too was readily broken by bending.

Example 2 Batting of acrylonitrile polymer mol percent) was blackened byheating in air at 230 C. for 15 minutes. The blackened cotton obtainedin this way was then heated in a nitrogen atmosphere at 1,000 C. for 1hr. The product retained its original form and was flexible. On theother hand, the product which was made merely by heating the samebatting in a nitrogen atmosphere at 1,000 C. for 1 hr. formed aconglomerate which was easily broken by a small force.

Example 3 A fibre made of copolymer of acrylonitrile 92 mol percent and2-methyl-5-vinylpyridine 8 mol percent was treated in the mannermentioned in Examples 1 and 2. Substantially the same results wereobtained.

Example 4 Woven fabric (plain weave; warp and woof yarn countings No.48, two-ply) made of yarns of acrylonitrile copolymer containing 4 molpercent of methyl acrylate was heated in air at 220 C. for 1 hr. andthen the blackened fibre was heated in nitrogen at 1,000 C. for 1 hr.The product was flexible and not broken even by bending to an angle of180 degrees. The woven fabric heated solely at 1,000 C. for 1 hr. wasbroken by bending to angle of 15.

Example 5 The same yarn as that used in Example 1 was blackened by beingheated in air at 220 C. for 30 minutes. Then it was buried in graphicpowder and graphitized at 3,000 C. The product was flexible, its tensilestrength being above 40 g./yarn. The same yarn was buried in graphiteand graphitized at 3,000 C. The product obtained in this way was verybrittle, its tensile strength being below 6 g./yarn.

What is claimed is:

1. A method for the preparation of flexible heat resistant and corrosionresistant fibre, comprising pretreating a fibre, which is to becarbonized and which is selected from the group consisting ofacrylonitrile homopolymer and acrylonitrile copolymer prepared from notless than 85 mol percent of acrylonitrile and not more than 15 molpercent of a monovinyl compound, by heating the fibre at a temperatureof from 180 to 550 C. in an oxygen containing atmosphere for a timesufficient to blacken the fibre',and then carbonizing the blackenedfibre at a temperature between 700 and 1200 C. for not less than onehour in an inert atmosphere to form a carbonized fibre. Y

2. A method according to claim 1 wherein said carbonized fibre is thengraphitized at a temperature between 1200 to 3000 C. in an inertatmosphere to form a graphitized fibre.

3. A method as claimed in claim 1, wherein the pretreatment heating iseffected for 5-60 minutes..

7 4' References Cited by the Examiner UNiTED "STATES PATENTS 2,799,9157/1957 Barnett et al. 8-115.5 X 3,011,981 12/1961 Soltes 252S023,027,222 3/ 1962 Wilkinson 8115.5 3,107,152, 10/1963 Ford et al.23209'.2 X

-, MILTON WEISSMAN, Primary Examiner.

OSCAR R. VERTIZ, Examiner.

E. J. MEROS, Assistant Examiner.

1. A METHOD FOR THE PREPARATION OF FLEXIBLE HEAT RESISTANT AND CORROSIONRESISTANT FIBRE, COMPRISING PRETREATING A FIBRE, WHICH IS TO BECARBONIZED AND WHICH IS SELECTED FROM THE GROUP CONSISTING OFACRYLONITRILE HOMOPOLYMER AND ACRYLONITRILE COPOLYMER PREPARED FROM NOTLESS THAN 85 MOL PERCENT OF ACRYLONITRILE AND NOT MORE THAN 15 MOLPERCENT OOF A MONOVINYL COMPOUND, BY HEATING THE FIBRE AT A TEMPERATUREOF FROM MONOVINYL COMPOUND, BY HEATING THE OXYGEN CONTAINING ATMOSPHEREFOR A TIME SUFFICIENT TO BLACKEN THE FIBRE, AND THEN CARBONIZING THEBLACKENED FIBRE AT A TEMPERATURE BETWEEN 700* AND 1200*C. FOR NOT LESSTHAN ONE HOUR IN AN INERT ATMOSPHERE TO FORM A CARBONIZED FIBRE.